'97 Dodge Dakota Oil Pressure Drop when Warm

Subject: '97 Dodge Dakota Oil Pressure Drop when Warm Date: Wednesday, December 06, 2006 12:30 PM
'97 Dodge Dakota 4x4 5.2L
I have been chasing this oil pressure problem around and decided to see what
this group thinks. The OP is 40+ when started and remains until normal operating temperature is achieved. It then drops down to ~20psi or the low range on the gauge, but not below the lower limit indicator. When under acceleration or load it sounds like lifter rattle. I replaced the sending unit because the old one wouldn't read the low signal and dropped the gauge to 0psi. New filter and oil (20W-50 Florida) and still not maintaining the pressure when normal operating temp. I read a post on a web site that explained the 'Thrust Bearing' was bad which allowed a 1/8" shift in the crank position and after replacing the thrust bearing (and I would expect the rest of the mains) the oil pressure drop when warm disappeared. I would think that if the thrust bearing was bad that it would have the pressure problem even when the engine was cold or just warming up. I can drive it 45, 55, and the pressure still remains at 40+ until it reaches N.O.T. and then drops to the lower range of the gauge (~20psi?). That makes me think along the lines of a viscosity problem or a pump that has worn impellers. IE. the oil remains thick enough for the pump to work at lower temperatures but as soon as the oil is hot and the viscosity drops the problem surfaces. Any comments on your experiences with fixing this problem would be appreciated. remove no spam to email
DJ
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DJ wrote:

That oil pressure drop sounds normal to me. If it were mine I'd put 10W-30 back in it and check the pressure again. If I still had 20 psi at idle hot I'd be happy. The "lifter rattle" noise may be caused by the spark plug wire routing. Try this: http://autorepair.about.com/library/a/1h/bl654h.htm
--
Ken



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OK. After I reinstalled the plug wires with the proper convolute and routing 98% of the knock is gone. I had previously rerouted the wires per All Data, but I didn't have the convolute at the time. The previous owner had the wires routed all wrong. Hopefully there wasn't much engine damage from premature crossfire. The oil pressure goes to the lower end of the range, but within the operating range. One more thing, would you recommend running an engine flush (kerosene) through to clean out the sludge? The 5.9L has 100,000 on it now and there is a littler lifter noise at higher RPM's. I bought the truck with 97,000 on it and when I changed the oil the first time the gauge dropped to 0 psi and the check gauges light went on and wouldn't work at idle until I replaced the oil sending unit.. It must have been a coincidence that the oil pressure sensor was bad, but functioning until the new filter put increased pressure on the oil sending unit. I have read in several other forums that the Dodge Dakota has been known to have oil pressure problems. However, it didn't really indicate which engines had the problem. It seemed the 3.9L was mentioned more than the others. I have the materials for the oil change, but wanted your opinion on the flush first. Thanks for making me go back and finish the wire routing with convolute. After many years working on engines, I couldn't believe the wire routing would cause that much knock. It definately sounded like mechanical damage! Thanks again Ken!
DJ

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I wouldn't recommend any kind of engine flush, I've had a fair amount of bad experiences with disturbing sludge.
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Cleaning out the sludge might cause some oil leaks. Sometimes when gaskets get old and cracked, sludge creeps in there to fill the voids. When you clean the sludge out the gaskets start leaking. I'd leave it alone.
--
Ken



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My 98' Dakota was having about the same problem. Turned out to be the brand new oil filter. Replaced it with a Wix filter and oil pressure shot up to the upper mark. However I think the drop is normal after the oil gets warm and engine comes to an idle, mine drops just below 40psi. I would not try the flush out the sluge, it may do more bad than good.
DJ wrote:

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Your post says 40 psi ?? First when it is cold you should get maybe 80 psi oil pressure If you do not Verify it with a mechanical oil pressure gauge. If low The only thing to do is CHECK THE BEARINGS. I ignored a oil pressure loss on a LA360 pre magnum had 20 at idle not its normal 40 psi ended up breaking the crank which I suspect was caused by the bad bearing clearences allowing the crank to flex
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My last truck was pretty high mileage. Castrol GX or GTX, or whatever it was. That was the only brand that quieted the rod knock longer than two or three days after an oil change. Please consider a different brand of oil.
My favorite mechanic likes Quaker State, but I didn't have as good a results as I did with Castrol. He'd had several experiences with people having low oil pressure, after an oil change at a Valvoline place. He'd drain the oil, put in Quaker State, and they'd be good to go.
Please try Castrol. Might be the answer.
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Christopher A. Young
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